This invention relates to a method for producing galvanized metal sheet or strip material having a zinc coating on one side only. More particularly, this invention relates to a method for treating zinc-coated metal strip or sheet material so as to remove the zinc coating from one side thereof while simultaneously depositing a substantially equivalent amount of zinc on the opposite side and at the same time preventing the formation of a zinc deposit on cathode means utilized in the process.
The use of galvanized metal sheet or strip material is conventional in many applications where corrosion resistance is important. However, in some cases, particularly when used in automobile body construction and the like, it is undesirable to have a zinc coating on both sides of the metal sheet or strip since such a coating has an undesirable effect on the weldability and surface finishing of the metal. In such instances it is important to provide a material having a galvanized surface on one side of the metal sheet, which side is generally unprotected otherwise, and a clean surface on the opposite side for efficient weldability and cosmetically acceptable surface finishing, such as painting.
The electrolytic methods proposed in the past for the production of such one side-galvanized material have all been characterized by the formation of a zinc deposit on cathode means. In the usual cases such deposits must be removed and various methods are employed for this purpose including reversing the polarity of the system, dissolving the deposits in acid, or by peeling. Whichever procedure is selected, this added operation in the process decreases its efficiency.